1. Industrial useful field
This invention relates to a flywheel assembly which absorbs vibration of input power.
2. Prior art and its problem
In FIG. 9 which is a schematic structural diagram of a conventional clutch disc, 10 is an engine input side and 12 is an output side from which a power is transmitted to a transmission, for example. A first-stage torsion spring 14a, a second-stage torsion spring 14b and a third-stage torsion spring 14c are interposed between the input side 10 and the output side 12, and specified torsion angle plays 14d and 14e are provided to the second-stage torsion spring 14b and the third-stage torsion spring 14c. Further, a first-stage hysteresis torque generating mechanism 16a, a second-stage hysteresis torque generating mechanism 16b and a third-stage hysteresis torque generating mechanism 16c are interposed therebetween in the same manner, and plays 16d and 16e are provided to the second-stage hysteresis torque generating mechanism 16b and the third-stage hysteresis torque generating mechanism 16c, respectively.
In the above-mentioned conventional embodiment, a torsion characteristic changes from a first-stage torsion characteristic Kd1 and a first-stage hysteresis characteristic Th1 which are both generated by the first-stage torsion spring 14a together with the first-stage hysteresis torque generating mechanism 16a, to a third-stage torsion characteristic Kd3 and a third-stage hysteresis characteristic Th3 which are both generated by third-stage torsion spring 14c together with the third-stage hysteresis torque generating mechanism 16c, with an increase in a torsion angle as shown by FIG. 10. However, this characteristic has the following disadvantage.
Namely, it is desired to set the first-stage torsion characteristic Kd1.about.third-stage torsion characteristic Kd3 to small values as a countermeasure against noises, such as, gear chattering generated from a transmission in its neutral position and gear chatterings generated from the transmission and a differential gear in their driving position. On the contrary, however, it is necessary to set the first-stage torsion characteristic Kd1.about.third-stage torsion characteristic Kd3 to large values as a countermeasure against low frequency vibrations.
Accordingly, the torsion characteristic of FIG. 10 is set up separately according to a characteristic required to each vehicle. Further, because requirements for noise and vibration control by clutches has become increasingly higher in recent years, often characteristics which can not be dealt with by conventional clutch structure are required. For example, conflicting countermeasures against noise and low frequency are required, simultaneously, as mentioned above.
Therefore, technologies have been developed where vibrations from engine are positively absorbed by the flywheel.
There are prior arts, as shown by FIG. 11, for example, where an auxiliary flywheel 26a and a damper 26b are interposed in series between a conventional clutch disc 20, a flywheel 22 and a crank shaft 24. The auxiliary flywheel 26a is installed in parallel with the flywheel 22 through a torsion spring as shown by FIG. 12.
With regard to such a flywheel assembly, the applicant of the present invention has developed a flywheel assembly as shown in FIG. 13 and has filed applications thereon, as hereinafter listed. Such flywheel assembly for patent includes a first flywheel 104 fastened to an engine crank shaft 100 and engaged and disengaged by a clutch disc 102, a second flywheel 106 installed concentrically with the first flywheel and set to a specified mass, a damper mechanism 108 resiliently coupling the both flywheels, and a friction damping mechanism 112 which transmits an output from the second flywheel 106 to a spline hub 110 of the clutch disc 102 and damps its vibration only when said clutch disc 102 contacts with the first flywheel 104. (Japanese Patent Application No. 60-44298, U.S. Pat. App. No. 836,365, now U.S. Pat. No. 4,751,993, West German Patent Application No. 36 07 398.9, French Patent Application No. 8603211, Korean Patent Application No. 86/1451).
The flywheel assembly of such patent application is further improved in the invention of the present application.
An inertial damper, set to a specified mass may be connected to a propeller shaft to damp torsional vibration of a so-called drive-transmission system from an engine output shaft to a driven wheel of automobile. In the present invention the torsional vibration of the drive-transmission system are dampened by a flywheel assembly rather than an inertial damper.
In the flywheel assembly of my aforementioned application, as shown in FIG. 13, a facing 116 of a friction damping mechanism 112 is connected to a bolt 118 of the second flywheel 106, so that it becomes necessary to form a hole 120 on the first flywheel 104 and a working range of the friction damping mechanism 112 is limited to the area of the hole 120.
Further, in case when a power of a starter motor is inputted from a ring gear 122 of the first flywheel 104 at the time of starting the engine, the power is transmitted through the damper mechanism 108 to a crank shaft; so that it is necessary to determine a spring characteristic of the damper mechanism 108 in accordance with a load of the starter motor to cause a small degree of freedom of design.
Moreover, in the third place, a disc spring 114 of the friction damping mechanism 112 is installed on the spline hub 110 and a connecting plate 119 which connects the facing 116 to the spline hub 110. The structure of the clutch disc 102 becomes complicated. Furthermore, the facing 116 is also fixed to the bolt 118 of the second flywheel 106 side, so that the flywheel assembly and the clutch disc 102 are required to be completely disassembled when the worn-out facing 116 is replaced with a new one and the replacement is difficult.